When a golf club head strikes a golf ball, a force is seen on the club head at the point of impact. If the point of impact is aligned with the center face of the golf club head in an area of the club face typically called the sweet spot, then the force has minimal twisting or tumbling effect on the golf club. However, if the point of impact is not aligned with the center face, outside the sweet spot for example, then the force can cause the golf club head to twist around the center face. This twisting of the golf club head causes the golf ball to acquire spin. For example, if a typical right handed golfer hits the ball near the toe of the club this can cause the club to rotate clockwise when viewed from the top down. This in turn causes the golf ball to rotate counter-clockwise which will ultimately result in the golf ball curving to the left. This phenomenon is what is commonly referred to as “gear effect.”
Bulge and roll are golf club face properties that are generally used to compensate for this gear effect. The term “bulge” on a golf club typically refers to the rounded properties of the golf club face from the heel to the toe of the club face.
The term “roll” on a golf club typically refers to the rounded properties of the golf club face from the crown to the sole of the club face. When the club face hits the ball, the ball acquires some degree of backspin. Typically this spin varies more for shots hit below the center line of the club face than for shots hit above the center line of the club face.
FIG. 1 illustrates the problem to be solved by the present invention. FIG. 1 shows a ball location with respect to the intended target when the golf ball is struck with a club having a constant bulge and roll radius. The nine rectangles indicate the ball location when struck in the respective heel, toe, center, high, center, low combinations. The fairway 124 is separated from the rough 126 by a fairway edge 120,122. The final ball location is shown with respect to an intended target line 118. The intended target line 118 is the line along which the golf club head center is aimed when the golf is at the address position. When the golf ball is struck in the high position, the golf ball tends to have a “left tendency” which means the ball's final resting position will be left of the target line 118. As illustrated by points 100, 102, and 104 shown in FIG. 1. When the golf ball is struck in the low position, the golf ball tends to have a “right tendency” which means the ball's final resting position will likely be to the right of the target line 118 as illustrated by points 112, 114,116 shown in FIG. 1. When a golf ball impacts the ball in the central horizontal portion of the face, the ball tends to come to rest on target relative to the target line 118 as illustrated by points 106, 108, 110 shown in FIG. 1.
A golf club design is needed to counteract the left and right tendency that a player encounters when the ball impacts a high or low position on the club head striking face.